Pulse frequency selective recorder



Feh 4, 1948. J. M. HOLLYWOOD 2,

PULSE FREQUENCY SELECTIVE RECORDER Filed Jan. 17, 1946 AMPLIFIER TRIGGERRECORDER CIRCUIT r n INTERMITTENTLY I In] ENERGIZED Z5 FILTER I9 F I .2INTERMITTENTLY G ENERGIZED a ig 13 27 TO RECORDER cmcun FROM TRIGGERCIRCUIT FIG.3 AG [souRcE' 5| s3-\ ess I. 5 6 RECORDING 29 59 DEVICE 3:FROM TRIGGER CIRCUIT & 40 FILTER nvvnvrok JOHN M. HOLLYWOOD BY.

A T TOR/V5 Y Patented Feb. 24, 1948 PULSE FREQUENCY SELECTIVE REcORDERJohn M. Hollywood, Washington, D. 0., assignor to the United States ofAmerica, as represented by the Secretary of War Application January 17,1946, Serial No. 641,841

1 Claim. (Cl. 234-15) This invention relates, in general, to electricalcircuits and more particularly to circuits for differentiating betweenpulsed signals of difiering pulse repetition frequencies.

It is often desirable to provide a circuit which will give an indicationwhen receiving pulsed signals of a particular pulse repetitionfrequency, hereinafter referred to as P. R. F., and another indicationwhen receiving pulsed signals of other P. R. F.s. It is an object,therefore, of this invention to provide a circuit which will produce anindication when pulsed signals of a particular P. R. F. are received.

It is a further object of this invention to provide a circuit which willgive a differing indication when pulse signals of P. R. F.s other thanthe desired are being received. It is a still further object of thisinvention to provide a circuit which will be activated only by thefundamental frequency of the pulse signals and not by harmonics thereof.

In general, this invention utilizes a trigger circuit followed by aconventional band-pass filter. Incoming pulses cause the trigger circuitto operate, thereby producing a square wave output, each half cyclebeing initiated by each incoming pulse. The filter is tuned to thesquare wave voltage frequency,-which in turn is one half the pulsefrequency of the desired incoming signals. Only pulses of twice theresonant frequency of the filter circuit will cause an indication.

Other objects features and advantages of this invention will suggestthemselves to those skilled in the art and will become apparent from thefollowing description of the invention taken in connection with theaccompanying drawing in which:

Fig. l is a schematic block diagram showing broadly my invention;

Fig. 2 is a schematic circuit diagram of a filter circuit; and

Fig. 3 is a schematic circuit diagram of a recorder circuit.

Referring now more particularly to Fig. 1, pulses from an externalsource appear at point II and are applied to amplifier l3. The output ofthe amplifier is applied to a trigger circuit l5 whose output in turn isapplied to a recorder ll. A filter circuit l9 may be switched in and outof the output of the trigger circuit l5 by means of the switch 2|.

The filter circuit might be, for example, similar to the one shown inFig. 2 in which the output from the trigger circuit l5 appears atterminal 22 and is connected through switching means 2| to filtercircuit l9 which is normally of the band-pass type. Output is taken atterminal 2?. Switching means 2| is used to switch the filter ill in andout of the circuit.

The recorder [7 might be, for example, similar to the one shown in Fig.3 in which the output of the trigger circuit l5 appears at terminal at,being coupled through capacitor 3| to the grids 33 and 35 of thyratrons3'! and 39, respectively. Resistor 40 returns the grids 33 and 35 toground. Potentiometer ll is connected between a' source of positivepotential and ground. The cathodes t3 and 45 of thyratrons 31 and 39 areconnected together and connected through resistor 4'! to arm 49 ofpotentiometer 4|. An A. C. voltage source is applied to primary winding5| of transformer 53. The secondary winding 51 is connected betweenplates 59 and BI of thyratrons 3'! and 39. The voltage at center tap 63of secondary 51 is applied to recording device 55. Resistor E1 isconnected between the center tap 83 and ground.

In operation, pulse signals from an external source are applied to theamplifier l3, amplified, and applied to the trigger circuit iii. Theoutput of the trigger circuit is a square-wave voltage each half cycleof which is initiated by each of the incoming pulses. Therefore, thefrequency of the square-wave voltage is one-half that of the frequencyof the incoming pulses. If switch 2| is closed and the filter circuit I9is tuned to the square-wave voltage, the filter l9 will transfer voltageof the fundamental frequency of the square-wave voltage to its outputconnections. Therefore the fundamental frequency voltage will appear atthe input of the recorder I! with substantially no attenuation. At otherfrequencies, however, the filter 19 will not transfer voltage to itsoutput connections and substantially no signal will appear at the inputto the recorder II. In the event that the resonant frequency of thefilter l9 coincides with a harmonic frequency of the square-wavevoltage, the recorder ll will not be actuated since it is designed torespond only to signals above a particular level.

Referring now to Fig. 3, with the filter l9 switched out, thesquare-wave output of the trigger circuit appears at point 29 and at thegrids 33 and 35. The plates 59 and GI are fed in pushpull, that is, thevoltage at plate 59 will be out of phase with plate Bl. Each thyratronwill conduct when its grid voltage is above cut-off and its platevoltage reaches the ignition voltage at the beginning of a positivecycle. Conduction will continue during the positive cycle at the plateuntil the extinction voltage is reached. Tube currents flow throughresistor 61 causing a pulsed voltage at twice the frequency of the A. C.source by the pulsed voltage appearing at the input of the recordingdevice 65. If desired, visual indication means may be used. Also, inpractice, the filter i9 is switched in and out of the .circuitat aregular rate by means of switch2lcontrolled by intermittently energizedrelay coil 23. It will be seen then that when a pulsed signal, ata P. R.F. for which this circuit was designed,

is received, switching the filter l9 in and but ofthe circuit will haveessentially no effect and the recording device 65 willrecordsubstantially a solid line. However, if the pulsed signalsreceived are at another P. R. the output of the recorder I! will be aseries. of regularly. spaced dashes, since the filter iSattenuates theoutputof trigger circuit i2- and effectively removes the. input to therecorder l1 when the switch 2iisin the position indicated in thedrawings,

It shouldbe noted that the amplitudeof the output of 'thetrigger circuitl5 is-of a constant value regardless of the amplitude of its: input. Theoutput I being essentially a a square-wave voltage will contain onlyodd-order harmonics and the third harmonic'will have an amplitudeone-third the amplitude ofthe fundamental. Therefore, if thepotentiometer 4i isset so that only signals above a value one-third ofthe fundamental frequency will cause the tubes 3'! and 39 to conduct, noharmonics will actuate the recorder H.

While there has been described what is at present considered to be thepreferred embodiment of this invention, it will be obvious to thoseskilled-intheart that various changes and modifications may be madetherein without departing from the scope of the invention as set forthin l the appended claim, and I claim all such changes andmodificationsas fall fairly within the spirit and scope of theinvention.

Wh is claim d i -A- combination for recording pulse signals includingsignals of predetermined pulse frequency, comprising, -a square wavegenerator controlled by successive pulses to generate successive halfcycles of square wave output, means to apply the output of said squarewave generator to a recorder alternately directly and through a filter,said filter having a ,pass band of one-half the predetermined pulsefrequency, whereby signals of said predetermined pulse frequencyarecontinuously recorded and signals of other pulse. frequencies are.intermittently recorded.

. QH HQL YW QD- Cox May 19, 1942 .I-Iansell "July.v 6, 1943 Number

